Infrared detector using a raman scattering medium



219,121 s@ K; l] M1905 y.

.i ngel, was;V A. Roms@ '3,204,105 /FPAgEDETECToR USING A RAMANSCATTERING MEDIM 'i Filed aan.' 2s. les;

WESLEY ROBINSN .Y -1NvENToR.

"RELATvlvE INTENslT-wf'f.

ttit'ed States @eredi @bce 'sientes' 3204105" Aug. :str1-ses excitedstate. This quantum energy separation corresponds to the frequency ofthe infrared radiation to be'Y INFRARED DETECTG'R. USING A RAMANmeasured. The Raman scattering medium is exposed to SCA'ITERlNG MEDIUMthe infrared radiation and this radiation induces, at least Wesley A,Robinson, El Segundo, Calif.,` assignat, by 5 intermittently, anonthermal equilibrium population dis mestre assignments, to ThompsonRamo Wouldridge tribution between the ground quantum energy state andIUC Ciel'imi om?, 2 C OI'POFBOD 0f 0h50 the first excited state; thisevposure results in an over- Filed Jim- 2-1, 1961, Ser; No. 84,233 vpopulation o moleculesin the first excited state. A beam` 23 Simms (CL25a-31) l l of electromagnetic radiation, preferably monochromatic 10`or narrow band, which for example 'may be in the visible This inventionrelates tothe electromagnetic radiation portion of the electromagneticradiation spectrum, is diamPCBOIl 3ft and, mOn- Pal'culafl, t0 mPfOVCrected to traverse the Raman scattering medium in a premethos of andarrangements for measuring the intensity selected direction. During thistraversal one of the possi o f preselected frequencies ofelectromagnetic radiationble interactions, between the photonsassociated with the The HCHSY f Certain ICQUCUCCS 0f @iCCYOmagDEC 15visible radiation and the molecules of the Raman scatter. radiation hasbeen, in the past, generally diicult to measing medium that are inthergt excited state, i5 a virtual um. In Pal'fcuial, "-1' Fangemns for'measuring the VI1- absorption ofthe photons by the molecules, Thephoton tensity of electromagnetic radiation in the infrared portionabsorbing molecule subsequeritiy eolapses down to the Of tho spectrumhave 110i aiWayS been 2S SCnSVe aS may ground state and thereby emitselectromagnetic radiation \`1 be desired and for some of the iowerinfrared frequencies 20 at a frequency slightly greater than the visiblefrequency. 'i there are, et present, only comparatively insensitive in-The difference in frequeiiey is an amount equivaient to theteIlSlt'ymeasuring deVlCeS. Thus,whlic lead SulpbCie,leat energy ,parationbetween the ground quantum energy' telluride, and other materials havebeen utilized in the 'ginie and the first excited state. (Thisufrequencydiffer- Pf-S fol' measuring the DCUSIY 0f ih e COmPBYHVCY ence, asstated above, is equivalent to the frequency of higher infraredfrequencies, and thermocoupacs and thcrthe infrared radiation that is tobe'measured.) This frernopiles for measuring these and lower infraredrequcnqueriey emitted from the molecules is termed the antif cies, sucharrangements have not provided the desired Stokes line. The intensity ofthis anti-Stokes iine de highly SCUSVS HCHCMOH 0f mensy- 111 COHTaS, Ol'ponds on the number of molecules of the Raman spectra electromagneticradiation vin the visible portion of tho that are in the rst excitedstate and are thus available for electromagnetic radiation spectrum,comparatively high the virtual absorption of photons. Thus, theintensity of detection etciency is realized, and very sensitivedetectors, the anti-Stokes line is proportional to the intensity of thesuch as solar cells and photomultiplcrs, are available. incidentinfrared radiation which increases the number f ACCOrfiingly, it 5S anObject Of this invention 10 provide of molecules at the firstexcited/state. Since the antian improved method of and means fordetecting the in Stokes line, in this examplefi's'also in the visibleportion tensity of preselected frequencies of electromagnetic radiaofthe electromagnetic radiation spectrum, a sensitive dcrector, 'such as asolar cell, photo multiplier, or the like,

tion.

1f S another ObJ'CC 0f this invention to prO'v/dc mis utilized to detectthe intensity of the anti-Stokes line. proved methods of and means formeasuring the intensity Thus, the measurement of the intensity of theanti-Stokesg of infrared radiation. line provides a measurement of theintensity of the in# it is yet another object o this invention toprovide im- 4@ cident infrared radiation. proved methods or' and meansfor converting variations in In another embodimentbf this inventionwherein it is the nter-Sill 0f SSCUOYUHDQC Tadiatm in 011 portiondesired to measure the intensity of a preselected bandwidth of theelectromagnetic spectrum to corresponding variaof infrared radiationrather than a single frequency, a tions in intensity of electromagneticradiation in another, Raman scattering medium is selected that has aband and mre easily meslll'bl, POIOH 0f the CCCYOmg" 45 quantum energyseparation between the molecules at the netic radiation spectrum. groundenergy vstate and a first ecited statc""The band The fOYEgGHS and YemdObjects are realized aCCOYdHg quantum energy separation corresponds tovthe infrared Y0 this IIVCUOH OY fS ndufn; 2 VTUH abSOFPOD 0f bandwidthto be measured. Upon the molecuies collapse photons, SSOCHlCd with 2PICSLlSCd ffecluency 0f elC- 'to the ground state from the t'irstexcited state, associated z UOmgP-@C Tdafm, b3' 2 Raman Scafefng medium5G with a virtual absorption of visible photons, there is an and thendetecting the intensity of the anti-Stokes line in emission of ananti-Stokes band having an intensity prothe electromagneticredifuon-eHt-iremitted from the portionartonhermnared bantrindtnintensity. nete-onori Raman SCaierug medium AS USCd herein, a' Raman ofthe intensity of the anti-Stoker band provides a meas Smile-Dg medium i5d'lned a5 a Coneco 0f Similar ure of t'ne intensity oftheincident'infrared bandwidth. molecules which have e known, preeleetefrequency The invention is expiained in greater detail in the fot-5';associated with' a quam'lm energy THISOH between WO lowing specicationtaken together with theaccompanying Efeselced quanlum energy Sti-93 0f hmOeCUC Thu drawings, wherein like reference characters refer to sim-1virtual absorption of the photons by molecules in the ilar elementsthroughout, and in whichi t S bisher of the Iwo energy States results inemission of elec- FIGURE 1 illustrates the apparatus associated with onetromagnetic radiation from the molecules at the anti-Stokes embodimentof this invention;

frequency; this emission oeeurs 2S the moieoules Collapse FiGURE 2 is aschematic illustration of eieetroiiiag-r v 'i0 ih@ lower 0f VHC IWO negyS'laesnetic radiation emitted from the Raman scattering medium' In oneembodiment or' this invention, where it is desired 0fF1GURE1;;md 1 tomeasure the intensity of e particular frequency of, for .FIGURE 3 is aschematic illustration of electromagexample flffafed radiation, a Rnmmcfleflflg medium 65 'netic radiation emitted from another Ramanscattering is selected that has a particular quantum energyseparamedium.

tion between the ground quantum energystae anda iirst '1 Referring nowtoFIGURE l, thereis shown an ar-' 'i 'i rangementxfor measuring theintcnsitylof a preselected frequency of electromagnetic radiation. A gascell 10, having walls `12 that are transparent to preselectedwavelengths of electromagnetic radi-ation, contains a Raman scatteringmedium 14. The Raman scattering medium 14 is maintained in the gas cellin a gaseous state. A lamp means 16, having transparent tube member 1S,is adapted to emit electromagnetic radiation 2G from a va porizablesubstance -22 contained within the tube` means 18. Thus, for example,the Ilamp 116 may be a sodium vapor lamp, mercury vapor lamp, or vthelike, and the substance 22 contained within the tube means =18 isinduced 'to emit the electromagnetic radiation-20 -by the inuence of a-high frequency magnetic eld generated by coimcans 24 which is poweredby signal generator 26. A retector means 28 directs the electromagneticradiation emitted from the lamp means 16 to traverse the Ramanscattering medium `14 in a preselected direction. Associated with -thelamp 16 is a filter means 30 which is adapted to Itransmit substantiallyonly energy ooncem tratcd in a single frequency. Thus,-if lamp -16 is asodium vapor lamp, the -filter 30 may be adapted to transmit iilteredelectromagnetic radiation 21 in the prominentv sodium -line at 5.0.91014 cycles per second; similarly, if the -lamp -16 were -a mercuryvapor lamp, the tilter 30 may be adapted to transmit as filteredelectro-magnetic radiation 21 substantially A only energy concentratedat 6.86 1014 cycles per second. A collimator 32 is positioned -tocollimate the filtered electromagnetic radiation 21 to providecollimated electromagnetic radiation 2.3, and a polarizer 34 ispositioned to polarize the collimated electromagnetic radiation 23 toprovide polarized electromagnetic radiation 25. Applicant has found thatpolarizing, which, for example, may be circular or plane polarization,aids the cfliciency o operation of this system and, in the preferredembodiment of this invention, the polarizer is included. However,satisfactory operation is also obtainable without utilizing thepolarizer 34. ln the arrangement shown on FIGURE l, the polarizedelectromagnetic radiation 2S traverses be Raman scatterin g medium 14-in a preselected direct-ion.

A cooling jacket 56 is provided adjacent the gas cell4 10 and -a coolant38, such as water, is pumped by pump means from reservoir 4Z through thecooling jacket 36 to maintain the Raman scattering medium A5.4 at apre-` selected temperature.

Electromagnetic radiation 44 is emitted from the Raman scattering medium.14 and a detection iilter 46 -is provided to receive the emittedelectromagnetic radiation 44 and transmits substantially only energyconcentrated in a preselected frequency 48. A detector 50 is positionedto receive the preselected irequency 48 and to generate a signalresponsive to variations lin the intensity of the preselected frequency48. This signal may be amplified by ampler 52 to provide an informationsignal at output 4 terminals 54 having an information content, such asmagnitude, proportional to variations in the intensity of thepreselected frequency 48.

In operation, this arrangement is utilized to measure the intensity of apreselected frequency of, for example, infrared radiation. Thispreselected frequency ot' electromagnetic radiatio.. is contained withinan incident beam of infrared radiation 56 which traverses the Ramanscat- -tering medium 14. The Raman scattering medium 14 is selected sothat the frequency associated with the energy separation between aground quantum energy state of the molecules comprising the .Ramanscattering medium .14 and an excited state, which for example may be therst excited. state, corresponds to the preselected frequency of infrared.radiation within the incident beam S6 whose Ain ing the Ramanscatteringmedium 14. ferred from the photons associated with thepreselected I 'of infrared radiation mpirtgcs on the m Energy 1s'transfrequency of infrared radiation to the molecules to establish, at leastintermittently, a greater population/o molecules rin the -rst excitedstate than is normally obtained Y Thuis, the preunder thermalequilibrium comditionsV selected frequency of infrared radiationincreases the number of molecules at the rst excited state and cle-Tf ifcreases the number of .molecules at the ground quantum energy state. 4

When the polarized electromagnetic radiation 25 naverses the Ramanscattering medium 14, [there are three main types of interactions thatmay take place between the photons associated with the polarizedelectromagnetic radiation 25 and the molecules comprising the Ramanscattering medium 14. There may bc an inelastic scattering as thephotons associated with the polarized electro- Y magnetic radiation 25impinge upon the molecules of the Raman scattering medium 14, in whichcase electromagnetic radiation 20' at substantially the same frequency uas polarized electromagnetic radiation 25 1s emuted from the Ramanscattering medium.

Another type of interaction may occur tons associated with the polarizedeltromagnetic radiation -25 undergo inelastic collisions with themolecules comprising the Raman scattering'medum 14. lf these photons:impinge upon a molecule of the Raman scatter ing medium 14 that isinitially'n the ground quantum energy state, energy is transferred fromthe photon to v the molecule and the molecule yis raised to the firstexcited state. For this type of nteraction, a photon is re-emitted at aslightly lower frcquency than the frequency of the polarizedelectromagnetic radiation and this frequency is Vtermed the Stokes line.ll'l'he ditrcrence between t'ne Stokes frequency and the polarizedelectromagnetic radii ation 2S -frequcney corresponds to the frequencyditicrence between thc ground quantum ener-gy state and the iirstexcited state of the ).'molecule which, as described above, is the:infrared frequency whose intensi-ty is to be measured. FIGURE 2 showsthis relationship. The Yline v is the frequency of the polarizedelectromagnetic radi. ation 2S which, lfor example, may be the sodiumline at 5.09)(1014 cycles per second. For example, .if the frc- 'quencyof infrared radiation whose intensity is to be 4 measured is 6.67 l01'f`cycles per second, gaseous N210 may be selected as the' Raman scatteringmedium. N20 has a frequency associated with the energy separationbetween the molecules at its ground quantum energy state and themolecules at its lfirst exctied state corresponding to 6.67 1013 cyclesper second. Thus, the fre quency of the Stokesfliue v' is separated fromthe sodium frequency v by an amount v=6.67X 1013 cycles per secl ond andtherefore has an absolute value of 4.42X1O1 fj cycles per second. Therelative intensity of the frequency v is very much greater than theStokes frequency v' due to a lower probability of the inelasticcollisions that give rise tcnsity is to be measured. This is termedash-arp line Y. quantum energy transition,'

The beam 56 -may traverse diumld in any arbitrary direction. intraversing the the Raman' scattering meto the Stokes frequency v'.

Another type of collision may taire place between the the photonsassociated with polarized electromagnetic radiation 2S andthe moleculesof the Raman scattering medium 14 at a rst excited quantum energy state.This ,type collision and the associated emission of electromag netteradiation may be termed an exohermic virtual absorptlon.

photon by the molecule at the rst excited state which sorption there isa collapse of the molecule to the ground vstate-and in this transition,from the first ,excitcd statef'! down to the' ground quantum energystate, there is an emission o electromagnetic radiation and thefrequency of this emitted elcctromagneti radiation 'isV equivalent? whenthe pho- Thisoccurs when these photons impinge upon i' a molecule tlfatis at the first excited state.

action there is a virtual absorption of the impinging in this inten Y tothe frequency of the i preselected temperature.

Applicant has found that Raman scattering medium other than gases mayalso be utilized in the practice of mpinging electromagnetic radiationplus the frequency associated with the energy difference between thefirst excited state and the ground quantum energy state. This is termedthe anti-Stokes line and is indicated on FIGURE 2 as the line v.' Thefrequency 5 emitted from the solid Raman scattering medium- 14th..:

As described above, detection of this anti-Stokes fre' quency andmeasurement of the intensity thereof provides difference between thefrequency g and the anti-Stokes c`line v is also v:6.67 1013 cycles persecond (for the above example) and, thus, the absolute value of theanti- Stokes line is 5.7:' 7 1O1 4 cycles per second.

Under thermal equilibrium conditions at, for example, C., there isnormally very few molecules of N20 at the first excited state andtherefore a very low probability of virtual absorption. Thus, theanti-Stokes line associated with the frequency v is normally very faint.However, under the inuence of the incident infrared radiation 55 which,as noted above, contains energy in a frequency corresponding to theenergy difference between the ground quantum energy state and the rstexcited state, the population of molecules at the irst excited state isvery greatly enhanced i roportigntothedntensity or /Iynumber of photonsat this" re-selected frequency of infrared radiation. Consequently, theintensity of the anti Stokes line is proportionately increased.

per second, the detector 50 may be a comparatively high efficiency typedetector such as a photoelectric cell or solar cell and, therefore, moreenergy per photon in thepreselected frequency 48 is available to thedetector 50 than Vif infrared type detectors were utilized to measurethe intensity of the incident infrared. frequency directly.

The most important competing mechanism in the arrangement, shown onFIGURE 1, that tends to reduce l the signal to noise ratio is thethermal relaxation of the molecules caused by molecular interactions.

One method of minimizing the thermal Vrelaxation is by maintaining theRaman scattering medium 1 4 at a preselected temperature that reducesthe probability of molecular nteractions. As shown on FIGURE 1 this maybe accomplished by circulating a cooling medium 3S to cool SX Thedetection lter 46 of FIGURE 1 is adapted to the Raman scattering medium14 and maintain it at the this invention. Thus, for example as shown onFIGURE 1a, a Raman scattering medium 14a that is in the liquid state iscontained within a sealed liquid container 10a v of polarized andcollirnated monochromatic radiation 25a I traverses the medium 14a ih apreselected direction. Operation of this embodiment is similar to thatdescribed in connection with the embodiment of FIGURE 1 andAelectromagnetic radiation 44a containing energy in a frequencycorresponding to an anti-Stokes frequency asfrom the liquidV Ramanscattering medium 14a. Measurernent of the intensity of this anti-Stokesfrequency provides a signal having a magnitude proportional to theintensity of the preselected frequency contained in the iny sociatedwith the monochromatic radiation 25a is emitted fof..4 I -Applicant hasalso found that there are liquid and solid cident electromagneticradiation 56a, as described above.

/fSlid'Raman scattering media may also be utilized in the practice ofthis invention: such an embodiment is shown on FIGURE ib. containingenergy in a preselected frequency, is incident 'upon a solid Ramanscattering medium 14b. A beam of I polarized andv collimatedmonochromatic radiationZSb Electromagnetic radiation 56b,'

incident infrared radiation.

traverses the solid Raman ation 44h, containing energy in an anti-Stokesfrequency Vassociated with the monochromatic radiation 25b, is

au information signal having a. magnitude proportional to thepreselected frequency contained with'theelectromagnetioradiation Sb.Table I below lists a few of the gaseous and liquid Raman scatteringmedia having asharp line quantum energy transition which may be utilizedTABLE 1 l' Raman scattering media havngsmrp line quantum energytransition n Raman y state 'scattering4 l Medium Gas N20. i gasggo(szapor).)` 1S V3 l'. 4 Gas Nns. puf' 5. 'Gu NDQ. s Liquid NH3-smo.7. Liquid s- Liquid CCn+Hz0. f

Applicant'has also found that the intensty'ofa prel selected bandwidthof, for example, infrared radiation may also bedetected in the practiceof his invention. In such an arrangement, a Raman scattering medium is?i selected that has a band quantum energy transition and.

the detection lter 46 of FIGURE l is adapted to transmit energy in apreselected frequency bandwidth rather than i -a single frequency. Theoperation of arrangements 'to f' measure the intensity of a preselectedbandwidth of inci-` f 1^ dent infrared radiation is substantially thesame as that; x described in connection with the embodiments of FIG-URES l, la and 1b.

Raman scattering medium 14 having a band quantum energy transition. Themolecules associated with this Raman scattering medium have a pluralityof closely adjacent rst excited states, termed substates, that differ xonly very slightly in the absolute value of the frequency associatedwtihthe transitions from the ground state..

Thus, incident infrared radiation 56 containingenergy in the preselectedinfrared'bandwidth induces an overpopulation of a plurality of firstexcited states. A virtual absorption between these molecules at thefirst excited substates results in an emission of electromagneticradiation in an anti-Stokes bandwidth, indicated on FIGURE i Thefrequency difference 6v between the fre quencyV of the polarizedelectromagnetic radiation 251 and any individual frequency within thebandwidth v" corresponds to the frequency associated with the transitionbetween a first excited subsate and the. ground quan` Thus, thedetection lter 46 transmits-f a preseleced frequency bandwidthcorresponding to v'r' tum energy state.

land the detector 50 detects changes in the intensity there- Ramanscattering media as well as gaseous Raman scat' tering media that may beutilized to detect a bandwidth' of A few of these-media are':

listed below in Table lI. In addition, the liquids of most of the gaseslisted in Table I also have band quantum e11- ergy transitions. .Y

scattering medium 14h' infa, preselected direction. `As a result,electromagneticrradi-- in the practice of this invention to measure theintensity of a preselected frequency of electromagnetic radiation.

- 7 rante 1r Raman scattering media having band quanlqm energy Atpressures over x atmospheres.

This invention will also operate without utilization of the Filter ofFIGURE l. In such a case, the beam of electromagneticradiation thattraverses the Raman scattering medium is not substantiallymonochromatic, as described above, but contains several frequencies ofelectromagnetic radiation. In such a situation, the intensity of theanti-Stokes line associated with any one frequency in the traversingelectromagnetic radiation is reduced because of the numerous similarinteractions with the photons at other frequencies. This somewhatreduces the signal to a noise ratio available inthe information signalat the terminals 54.

ln the preferred embodiment of this invention, tie detection lter 46'and detector S0 are positioned to intercept electromagnetic radiation 44that is emitted from the Raman scatering medium 14 in a directionsubstantially perpendicular to the direction of the polarizedelectromagnetic radiation 25 as this tends to increase the sensitivityof the detection. However, other directional :1rrangements of thedetection lter 46 and detector 51') may be utilized.

Those skilled adaptations-of applicantjs invcntion"F example, the Ramanscattering effect described above is known to extend well into the I-ray region and, therefore, applieant's invention may be utilized todetect the intensity o frequencies other than infrared. Therefore, it isintended that the description of the embodiments 4herein* presented beconsidered as illustrative only and the appended claims are intended tocover all adaptations and modifications that do Vnot depart from thetrue scope and spirit of applicants invention.

Whatis claimed as new and is desired to be secured by Letters Patent ofthe United States is:

1. In combination: a Raman Scattering medium having a first quantumenergy level and a second quantum energy level higher than said firstquantum energy level;

`wall means coupled to said Raman scattering medium for receivingincident electromagnetic radiation having energy in at least onefrequency corresponding to the energy separation between said first andsaid second quantum energy levels of said Raman scattering medium; saidwall means -associated with said Raman scattering in the art vrill ndmany variations and j Raman scattering medium for maintaining said Ramanscattering medium at a preselected temperature; detecf tion filter meansconnected medium to filter electromagnetic radiation emitted from saidRaman scattering medium in a-direction substantialiy perpendicular tosaid preselected direction to transmit substantially only energyconcentrated in a frequency corresponding to the anti-Stokes frequencyof said preselected frequency; detection means coupled to said detectionfilter means for selectively detecting the intensity of said anti-Stokesfrequency; and signal generating means coupled to said detection meansfor generating a signal having a magnitude proportional to the intensityof said "r--- --dctected anti-.Stokes frequency.

2. The arrangement defined in claim 1, wherein said 4 polarizing meanscircularly polarizes said collimated beam of electromagnetic radiation.

3. The arrangement defined in claim 1, wherein 'said' 24": polarizingmeans plane polarizes said collimated beam of electromagnetic radiation.

4. In combination: a a tirst quantum energy level and a second quantumenergy level higher than said first quantum energy level; wall meanscoupled to said Raman scattering medium for reg5 ceiving incidentelectromagnetic radiation having energy in at least one frequencycorresponding to the energy scparation between said tirst and saidsecond quantum energy levels' of said Raman scattering medium; said wallmeans associated with said Raman scattering medium causing said incidentelectromagnetic radiation to traverse said Raman scattering medium; lampmeans for generating a beam of electromagnetic radiation; filter meanscoupled to said lamp means for filtering said electromagnetic radiationto transmit substantially only energy concentrated in a preselectedfrequency; collimating means-coupled to said lilter means, forcollimating said ltered beam of electromagnetic radiation; means fordirecting said collimating beam-of electromagnetic radiation to traversesaid Raman scattering medium in a preselected direction; detectionfilter means connected to said Raman scatter- -ing--medium-todiffer-electromagnetic radiation emitted from said Raman scatteringmedium in a direction substantially perpendicular to said preselecteddirection to transmit substantially only energy concentrated in afrcquency corresponding to the anti-Stokes frequency of saidlpreselected frequency; and detection means coupled to saidr detectionfilter means for selectively detecting the intensity of said anti-Stokesfrequency. Y

S. Ther arrangement defined in claim 4, wherein /said preselectedfrequency is in the visible portion of the elec-.

tromagnetic spectrum.

6. In combination:

for receiving incident electromagnetic radiation having to said Ramanscattering' 1 Raman scattering medium having a Raman scattering mediumhavmg a rst quantum energy level and a second quantum Y energy levelhigher than said first quantum energy levei;.

energy in at least one frequency corresponding to the -v energyseparation between said first and said second quantum energy levels ofsaid Raman scattering medium', said 6G wall means associated with saidRaman scattering medium medium causing said incident electromagneticradiation to traverse said Raman scattering medium; lamp means i' forgenerating-a beam of electromagnetic radiation; filter means coupled tosaid lamp means for filtering said electromagnetic radiation to transmitsubstantially only energy concentrated in a preselected frequency;collimating means coupled to said filter means for collimating saidfiltered beam of electromagnetic radiation; polarizv ing means coupledto said collimating means for polarizing said collimated beamofclectromagnctic radiatiom' means for directing said polarized beam ofelcctromagnctic radiation to traverse said Raman scatteringmcdium f in'apreselected drcctio cooling means coupled tosaid causing said incidentelectromagnetic radiation to traverse said Raman scattering medium;means for generating a substantially monochromatic, collimated beam ofelectro-V magnetic radiation in a beam traversing said Raman scatvtering medium in a preselected direction; detection means disposed inaradiation receivable relationship with rcspect to said Raman scatteringmedium for selectively detecting the intensity of at least onepreselected anti-Stokes. 7o c radiation emitted from said Ramanscattering medium; and signal generating means v coupled to saiddetection means for generating an inforfrequency of electromagneo mationsignal havinf1 fm informe-ion content proportional to said detected 'i.sity ci sara preselected anti-Stokes frequency of elccnomagneric:radi-:tiem Y v j. 11 Stokes frequency, whereby irradia scatteringmedium by electromagnetic radiation having energy in a frequencybandwidth corresponding to said band quantum energy transition increasesthe intensity of said anti5tokes line.

15. In combination: a gas cell having walls defining a cavity and saidwalls transparent to preselected wavelengths of electromagneticradiation; a Raman scattering medium in the gaseous state containedwithin the cavity and said Raman Yscattering medium having a bandquantum energy transition between a first quantum energy 4state l.and asecond quantum energy state higher than. said rst quantum energy state;wall means for receiving incident electromagnetic radiation havingenergysin a frequency band corresponding to said band energy` transitionbetween said first and said second quantum energy states of said Ramanscattering medium; said wall means) causing said incidentelectromagnetic radiation to traverse said Raman scattering medium; lampmeans for generating a beam of electromagneticradiation; fitter meanscoupled to said lamp means for filtering said electromagnetic radiationto transmit substantiallywnly energy concentrated in a tion of` saidRaman preselectedfrcquency; collimating means coupled to said filtermeans for collimating saidqfiltered beam of electromagnetic radiation;means for directing said coilimated beam of electromagnetic radiationtotraverse said Raman scattering medium iri a preselected direction;detection filter means connected to said Raman scattering medium to lterelectromagnetic radiation emitted from said Raman scattering medium in adirection substantially perpendicular to said preselected direction totransmit substantially only energy concentrated in a frequencycorresponding to the anti-Stokes frequency of said preselectedfrequency; and detection means coupled to said detection lter means forselectively detecting the intensity of said anti-Stokes frequency. I 16.in combination: a scaled container means having walls defining a cavityand said walls transparent to preselected wavelengths of 4electromagnetic radiation; a Raman scattering medium in the liquid statecontained within said cavity and said Raman scattering, v'medium havinga sharp line quantum energy transition between a rst quantum energystate and a second quantum encrgy state higher than said first quantumenergy state and said sharp line quantum energy transition correspondsto an infrared frequency; wall means for receiving incident.electromagnetic radiation having energy in at least one frequencycorresponding to the separation between said first quantum energy stateand said secondquanturn energy state; said wall means associated withsaid Raman scattering medium causing said incident electromagneticradiation to traverse said Raman scattering medium; lamp means forgenerating a beam of electromagnetic radiation; filter means coupled tosaid lamp means for filtering said electromagnetic radiation to transmitsubstantially only energy concentrated in a preselected visiblefrequency; collimating means coupled to said filter means forcollimating .said filtered beam of electromagnetic radiation; polarizingmeans coupled to said collimating `"means for polarizing said collimatedbeam of electromagmagnetic radiation having energy-in a frequencycorresponding to said sharp line quantum energy transition in- A creasesthe intensity of said antitokes line.

17. In combination: a sealed container means having walls defining acavity and said walls transparent to preselected `wavelengths of`electromagnetic radiation; a 1

Raman scattering medium in theliquid state contained.

within said cavity and said Raman scattering medium having a sharp linequantum energy transition between a first quantum energy state and asecond quantum energy state higher than said first quanlurncnergy state;

wall means for receiving incident electromagnetic radiation havingenergy in at least one frequency corresponding to the separation betweensaid first quantum energy j state and said second quantum energy state;said wall t.

mer-.is associated with said Raman scattering medium causing saidincident electromagnetic radiatiOrttQYe said Raman scattering medium;lamp means for generating a beam of electromagnetic radiation; filtermeans coupled to said lamp means for filtering said electromagneticradiation to transmit substantially only energy conentrated in apreselected frequency; collimating means coupled to said filter meansfor collimating said filtered beam of electromagnetic radiation; meansfor directing said collimated beam of electromagnetic radiation totraverse said Raman scattering medium in a preselected direction;detection filter means connected to said Raman l -to transmitsubstantially only energy concentrated in a frequency corresponding tothe anti-Stokes l said preselected frequency; and detection meanscoupled netic radiation; means for directing said polarized beam t ofelectromagnetic radiation to traverse said Raman scat tering medium in apreselected direction; cooling means s coupled to said Raman scatteringmedium for maintaining i said Raman scattering medium at a preselectedtemperature; detection filter means connected to said Raman scatteringmedium to filter electromagnetic radiation emitted from said Ramanscattering medium in a direction subs to said detection filter means forselectively detectingv y the intensity of said anti-Stokes frequency;

18. In combination: a scaled container means having walls defining acavity and said walls transparent to preselected wavelengths ofelectromagnetic radiation; a Raman scattering medium in the liquid statecontained within said cavity and said Raman scattering medium having aband quantum energy transition corresponding to a frequency band in theinfrared portion of the electromagnetic radiation spectrum between afirst quantum energy state and a second quantum energy state higher thansaid rst quantum energy state; wall means for receiving incidentelectromagnetic` radiation having energy in a frequency bandcorresponding to said band energy transition between said first and saidsecond quantum cni ergy states of said Raman scattering medium said wallmeans causingsaid incident electromagnetic radiation to traverse saidRaman scattering medium; lamp means for generating a beam or'electromagnetic radiation; filter means coupled to said lamp means forfiltering said elec-4 tromagnetic radiation to transmit substantiallyonly energy concentrated in a preselected visible frequency; col

limating means coupled to said filter means for Collimaty 'l i ing saidfiltered beam of electromagnetic radiation; polar-` izing means coupledto said collimating means for polarizing said collimatcd beam ofelectromagnetic radiation,

means for directing said polarized beam of electromag-r 1- neticradiation to traverse said Raman scattering medium in a preselecteddirection; cooling means coupled to said` g Raman scattering medium formaintaining said Raman l i Y' scattering, medium at a preselectedtemperature; detection ,v filter means connected to said Ramanscattering medium to filter electromagnetic radiation emitted from saidRaman scattering medium in a direction substantially' perpendicular tosaid preselected direction to transmit substantially only energyconcentrated in a frequency cor responding to the anti-Stokes :requencyof said preselected .4 I frequency; detection means coupled to saiddetection filter f A Stokes frequency; and signal generating meanscoupled l to said detectionr mea-ns for generating a signal having a.magnitude proportional to the intensity of said detected anti-Stokesfrequency, whereby irradiation of said Raman scattering medium byelectromagnetic radiation having energy in a frequency bandwidthcorresponding to said band quantum energy transition increases theintensity of said anti-Stokes line.

19. In combinationa sealed container means having* walls defining acavity and said walls transparent to preselected wavelengths ofelectromagnetic radiation; a Raman scattering medium in the. liquidstate contained within said cavity and said Raman scattering mediumhaving a band quantum energy transition between a tirst quantum energystate and a second quantum energy state higher than said tirst quantumenergy state; wall means for receiving incident electromagneticradiation having energy ecting tbe intensity of said anti` i i in afrequency band corresponding to said band energy transition between saidtirst and said second quantum energy states of sai-d Raman scatteringmedium; said wall means causing said incident electromagnetic radiationto traverse said Raman scattering medium; lamp means for generating abeam of electromagnetic radiation; lter means coupled to said lamp meansfor filtering said electromagnetic radiation to transmit substantially`only energy concentrated in a preselected frequency; collimating meanscoupled to said filter means for collimating said filtered beam ofelectromagnetic radiation; means for directing said collimated beam ofelectromagnetic radiation to traverse said Raman scattering medium in apreselected direction; detection lter means connected to said R manscattering medium to filter electromagnetic radiation emitted from saidRaman scattering medium in a direction substantially perpendicular tosaid preselected direction to transmit substantially only energy concentrated in a frequency corresponding to the anti-Stokes frequency of saidpreselected frequency; and detection means coupled to saidvdetectiontilter means for selectiveassociated with said Raman scattering mediumcausing said incident electromagnetic radiation to traverse said Ramanscattering medium; lamp means for generating a beam of electromagneticradiation; filter means coupled to said lampmeans for filtering saidelectromagnetic radiation to transmit substantially only energyconcentrated in a preselected visible frequency; collimating.

means coupled to said litter means for collimating said filtered beam ofelectromagnetic radiation; polarizing rncans coupled to saidcollim'atlng means for polarizing lecte'd temperature; cetection iiltermeans connected to` said collimated beam of electromagnetic radiation;means said Raman scattering medium to filter electromagnetic fordirecting said polarized beam of electromagnetic ra diation to traversesaid Raman scattering medium in a preselected direction; cooling meanscoupled to said Raman scattering medium for maintaining said Ramanscattering medium at a preselected temperature; detection x filter meansconnected to said Raman s:attering medium i ly detecting the intensityof said anti-Stokes frequenrzyg@VY to tilter electromagnetic radiationemitted from said Rat- -manscattering medium in a directionsubstantially perpendicular to said preselected direction to transmitsubstantially only energy concentrated in a frequency corresponding tothe anti-Stokes frequency of said preselected frequency; detection meanscoupled to said detection filterv means for selectively detecting theintensity of said anti-- Stokes frequency; and signal generating meanscoupled to said detection means for generating a signal having amagnitude proportional to'Y man scattering medium oyelectromagnetic*radiationhavring energy In a frequency corrc'spondng'tosaid sharp line quantum energy transition increases the intensity ofsaid anti-Stokes line.

21. In combination: a Raman scattering. medium-- inl' I the solid statehaving a sharp line quantum energy transltion between a tirst quantumenergy state and a second quantum energy state higher tran said yfirstquantum enf i ergy state; wall means .for receiving incidentelectromagnetic radiation having energy in'at least one frequencycorresponding to the separation between said rst quantum energy stateand said second quantum energy state; said wall means associated. withsaid Raman scattering medium causing said incident electromagneticradiation to t traverse said Raman scattering medium; lamp means forgenerating a beam of electromagnetic radiation; lter Y means coupled tosaid lamp means for ltering said elec- Y tromagnetic Vradiation :otransmit substantially only energy concentrated in a preselectedfrequency; collimating means coupled to said filter means forcollimating said filtered beam of electromagnetic radiation; means fordi.- recting said collimated beam of electromagnetic radiation totraverse said Raman scattering medium in a preselected direction,detection lter means connected to said Raman scattering medium to filterelectromagnetic radiation emitted from said Raman scattering medium inardirection substantially perpendicular to said preselected direction totransmit substantially only energy concentrated in a l frequencycorresponding to the anti-Stokes frequency of Asaid preselectedfrequency; and detection means coupled to said detection filter meansfor selectively detecting tite intensity oisaid anti-Stokes frequency.

2-2. In combination: a Raman scattering mediuml in the`- solid statehaving a band quantum energy transition corf responding to an .infraredfrequency band between a first quantum energy state and a second quantumenergy state higher than said tirst quantum energy state; wall means forreceiving incident electromagnetic radiation having' energy in afrequency band corresponding to said bandenergy transition between saidrst and said second quan- 'tum energy states of said Raman scatteringmedium; said I wall means causing said incident electromagnetic radia'tion to traverse said Raman scattering medium; lamp means for generatinga beam of electromagnetic radiation; filter means coupled to said lampmeans for filtering' said electromagnetic radiation to transmitsubstantially' only energy concentrated in a preselected visible free`vrquency; collimating means coupled to said filter means for collimatingsaid tiltered beam of electromagnetic rav diation; polarizing meanscoupled to said collimating means for polarizing said collimated beam ofelectromagnetic radiation; means for directing said polarized beam ofelectromagnetic radiation to traverse said Raman scattering medium in apreselected direction; cooling means coupled to said Raman scatteringmedium for' maintaining s aid Raman .scattering medium at a'presefradiation emitted from said Raman scattering medium in signal generatingmeans coupled to said detection means for generating a signal having amagnitude proportional tothe intensity of said detected anti-Stokesfrequency, v whereby irradiation of said Raman scattering medium byelectromagnetic radiation having energy in a frequency bandwidth'correspondingto said band quantum energy transition increases theintersityvor' said anti- Stokes line;LA 1

.23. ln combination: a-Raman scatteringmedium in the intensity saiddetected I anti-Stokes frequency, whereby irradiation of said Rathesolid state having a-bttntl quantum energy transition:V i v ReferencesCited by'tlie Examiner between a first quantum energy state and a secondquan- 1 .f' l

tum energy state higher than said rst quantum energy n "UNITED STATESyA-[ENTS t ing w said band energy transition between and rst and l 306-.959 11/62 Sclar 25o- 83.3

tering medium; said wail means causin said incident l i -lelectromagnetic radiation to traveise sai Raman scat- QIILR REFERENCESi" tering medium; lamp means forfgenerating a beam of 10 Bell etal.:Optical Detection of Magnetic Resonance: electromagnetic radiation;lterff'means coupled to said in Alkali Metal Vapor, Physical Review,SCPL 15, 1957, 4 1 lamp means for filtering said electromagneticradiation PP- 1559 l0 1555- Y to transmit substantially only e'nergyconcentrated in a Hbbcn The Raman Ell-@Ct and Us Chemical ISPPHCIT4preselened frequency; collimating means coupled to said ONS, RnhOld,1939 (Chapter 2 ICCd UT- i filter means for collimating said filteredbeam of electro- 15 B10-nii "Optical PUmPHE, SCCDIC Amefian, OC'

magnt'ic radiation; means for directing said collimated IObr 1960-Vl gbeam of electromagnetic radiation to traverse said Ra- Jelley: TimeDiscrimination in Solid-State Infrared Y man scattering medium in apreselected direction; detec- QUHDiUm Couplers," Journal 0f AppliedPhysics -lUiY tion tiltcr means connected to said Raman scattering 1960,pp- 1145 and 1145 s medium to lter electromagnetic radiation emittedfrom V20 SOChCf "High RCSOUOH Raman SPeCll'OSCOPy,"PUbsaid Ramanscattering medium in a direction substantially lishd in AdVanCBS il!SPCCU'OSCUPY, IIHCYSCSDC: PU'UlShv .perpendicular tc said preselecteddirection to transmit 35,1951 I Y `f substantially orJy energyconcentrated in a frequency 1 corresponding to the anti-Stokes frequencyor said prese- RALPH G* NELSON "mary Emml'r ...-z lected frequency; anddetection means coupled to said 25 RICHARD M, WOODi ARCI-HE R BORCHELT,i detection filter means/for selectively detecting the in- V Y5,;mmneI-5,l tensity of said anti-Stokes frequency. t s v` f fv`v`""-l'

1. IN COMBINATION: A RAMAN SCATTERING MEDIUM HAVING A FIRST QUANTUMENERGY LEVEL AND A SECOND QUANTUM ENERGY LEVEL HIGHER THAN SAID FIRSTQUANTUM ENERGY LEVEL; WALL MEANS COUPLED TO SAID RAMAN SCATTERING MEDIUMFOR RECEIVING INCIDENT ELECTROMAGNETIC RADIATION HAVING ENERGY IN ATLEAST ONE FREQUENCY CORRESPONDING TO THE ENERGY SEPARATION BETWEEN SAIDFIRST AND SAID SECOND QUANTUM ENERGY LEVELS OF SAID RAMAN SCATTERINGMEDIUM; SAID WALL MEANS ASSOCIATED WITH SAID RAMAN SCATTERING MEDIUMCAUSING SAID INCIDENT ELECTROMAGNETIC RADIATION TO TRAVERSE SAID RAMANSCATTERING MEDIUM; LAMP MEANS FOR GENERATING A BEAM OF ELECTROMAGNETICRADIATION; FILTER MEANS COUPLED TO SAID LAMP MEANS FOR FILTERING SAIDELECTROMAGNETIC RADIATIN TO TRANSMIT SUBSTANTIALLY ONLY ENERGYCONCENTRATED IN A PRESELECTED FREQUENCY; COLLIMATING MEANS COUPLED TOSAID FILTER MEANS FOR COLLIMATING SAID FILTERED BEAM OF ELECTROMAGNETICRADIATION; POLARIZING MEANS COUPLED TO SAID COLLIMATING MEANS FORPOLARIZING SAID COLLIMATED BEAM OF ELECTROMAGNETIC RADIATION;